This study presents three dual-band lowpass-bandpass filters. The first handles lowpass and bandpass bands through its fifth-order and third-order Chebyshev filter responses, respectively. This filter uses three circuits to achieve flexibility in cutoff frequencies and fractional bandwidths. The second is a higher-order filter: it is a dual-band filter with ninth-order lowpass and fifth-order bandpass responses. In general, an extra 50-transmission line might be required to connect each port conveniently to an external circuit for the first or second proposed filter, which could increase the circuit area. The third is a dual-band filter with a λ/4 impedance transformer near each port to facilitate connections with external circuits. Each of the proposed dual-band lowpass-bandpass filters has a systematic design procedure when the lowpass and bandpass band responses are given separately. In addition, the proposed filters can provide rapid prediction through the use of ideal circuit simulations instead of full-wave simulations.

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